VS Code:
Cmd + / = Comment/uncomment code
Cmd + S = Save document
Shift + Opt/Alt + ↓  = Duplicate lines

Browser:
Cmd + Shift + R = Reload (full reload w. asset files)

* Cmd = Ctrl on PC

Screenshots on Mac:
Shift + Cmd + 4 (snippet)
Shift + Cmd + 3 (full screen)